The melting i.sup.2.t and the peak of the let-through current of a current-limiting fuse depend primarily on the metal of which its fusible element or elements consist, and on the cross-sectional area of the points of smallest cross-sectional area of its fusible element, or elements. Since it is often necessary to minimize the melting i.sup.2.t and the peak of the let-through current, the point or points of smallest cross-sectional area of fusible elements must often be reduced to such an extent as to largely deprive the fusible elements of their dimensional stability. This makes it extremely difficult to handle the same, in particular to assemble the same with the other constituent parts of fuses, and to prevent damage to the points of minimal cross-sectional area, or necks, of such fusible elements.
Current-limiting fuses which have virtually point-shaped necks are disclosed in U.S. Pat. No. 2,665,348 to Frederick J. Kozacka; Jan. 5, 1954 for CURRENT-LIMITING FUSE. The above design is relatively complex and costly to manufacture, and it does not lend itself to applications wherein each fusible element must have a relatively large number of serially related points of drastically reduced cross-sectional area, and wherein a plurality of such elements must be combined in a single fuse structure. Another serious limitation of the above design consists in that there is no immediate physical engagement between the arc-extinguishing granular filler, or quartz sand, and the points of arc inception of the fusible element. Another limitation of the above design consists in that the granular arc-quenching filler is not in immediate physical engagement with the portions of the arc which result from the burnback of the fusible element.
Acceptance of these and other drawbacks in prior art current-limiting fuses were the price that had heretofore to be paid for drastic reduction of the cross-sectional area of the necks of the fusible elements thereof.
The present invention provides structures including fusible elements which have points of drastically reduced cross-sectional area and which fusible elements are not subject to the limitations of prior art fusible elements of this description.
SUMMARY OF THE INVENTION
The invention refers to lattice structures intended as components of electric fuses. The lattice structures comprise fusible elements and insulating supports therefor. To be more specific, a structure embodying this invention includes a fusible element in ribbon-form having a plurality of serially related points of drastically reduced cross-sectional area each formed by a pair of juxtaposed substantially V-shsped incisions. A structure embodying the invention further includes a substantially planar strip of electric insulating material arranged in spaced relation and substantially parallel to said fusible element, said strip having a plurality of arms projecting transversely therefrom and each supporting said fusible element at a region situated between said points of drastically reduced cross-sectional area.